AUTOMATED IOL INJECTION

[caption id='attachment_1318' align='alignright' width='400' caption='IOL implantation through a 1.9mm incision. Above: Monarch injection. Considerable pressure applied to keep the tip of the cartridge in contact with the nasally rotated globe. Below: AutoSert injection. Less pressure applied because the eye can be stabilised with second instrument'][/caption]

When operated at higher injection speeds, a new motorised IOL injector stretched small corneal incisions about half as much as a popular manual injector, David Allen FRCOphth, Sunderland, England, UK, told the XXIX Congress of the ESCRS.

The motorised AutoSert (Alcon) device enables one-handed injection, freeing the other hand to stabilise the globe. It also eliminates the sudden drop in plunger resistance that can result in overshooting with a manual injector, Dr Allen noted.

“The device is easy to use, it allows a much greater degree of control than the Alcon Monarch III manual injector, and when used at this fast setting we find it has statistically significantly less incision stretch,†Dr Allen said.

However, more research is needed to determine if decreasing incision stretch correlates with better wound integrity and less postoperative leakage or reduced surgically induced astigmatism, he added.

As cataract surgical incisions get smaller IOL insertion challenges are growing, Dr Allen said. The AcrySof D cartridge is designed for the AcrySof IQ IOL, and is specified for incisions down to 2.4mm, or 2.2mm with incision assist. But many surgeons go lower, to 2.0mm or even 1.8mm incisions, he noted.

However, these small incisions require holding the injector tip steady against the moving wound throughout the injection, Dr Allen said.

“This can result in a rather less-than-aesthetic procedure – it is as if you are trying to push the eye through the nose into the other socket to maintain apposition so the injection doesn’t fail.â€

Inserting an instrument in a sideport helps stabilise the globe. But it also requires a single-handed injector, Dr Allen said.

“The problem with a single-handed injector is that significant injection force is required to compress the lens through the small cartridge. You have to increase the pressure on the plunger, but once the lens leaves the cartridge, the force required rapidly drops off and there is a danger of overshoot.â€

Studies show that up to 15 Newtons are required to push the widest part of the lens through the smallest cartridges, he added.

The AutoSert injector was designed to apply a steady force, enabling insertion with one hand and stabilisation with the other. Over nine months prior to its commercial release in late 2011, Dr Allen and his colleagues tested it against the manual Monarch III to determine if it stretched incisions less.

The study involved 256 patients and three injection sizes, 1.8mm, 2.0mm and 2.2mm. Eyes were injected manually, or using the automated injector at a slow speed of 1.5mm/second or a fast speed of 4.4mm/second. To estimate incision stretch during surgery, wounds were measured at the end of irrigation and aspiration, and again after the lenses were inserted.

For pre-injection incisions of 1.9mm, the mean enlargement with manual injection was 0.17mm, with slow auto injection 0.14mm and fast auto injection 0.10mm. The difference between the manual and fast auto result was statistically significant, Dr Allen reported. Similar results were observed with larger incisions, with a 2.2mm pre-injection wound stretching a mean of 0.11mm manually and 0.04mm with fast auto.

Overall, 42 fast auto insertions resulted in no incision enlargement, compared with 15 for slow auto and eight for manual. Even through the smallest 1.9mm incisions, the fast auto sometimes created no enlargement while the slow auto and manual always did.

Conversely, the fast auto had the lowest incidence of stretching an incision by more than 0.1mm, with four overall compared with 26 for manual and 18 for slow auto insert. For 1.9mm pre-insertion incisions, only three fast auto incisions stretched 0.1mm or more compared with seven and nine for manual and slow auto incision. No incision 2.1mm or larger was stretched more than 0.1mm by the fast auto insertion.

Added seconds

Studies presented by Christer Johansson MD, Kalmar, Sweden, largely confirmed Dr Allen’s findings. In a study of 30 eyes with IOLs inserted with a manual Monarch III and 30 eyes with the AutoSert at 2.5mm/second, all with 2.0mm incisions, the automated eyes had less mean wound stretch after insertion, about 0.05mm vs. 0.11mm. Mean incisions size and wound stretch differences were statistically significant at p<0.001, Dr Johansson said.

However, automated insertion at 2.5mm/second took longer than manual by about 14 seconds, with a mean of 38.7 seconds compared with 25.1 seconds, he noted.

In a second study, Dr Johansson also found that speeding up auto insertion to 4.4mm/second reduced wound stretch. In two groups of 30 patients each, lenses inserted at 4.4mm/second had a mean wound stretch of 0.020mm compared with 0.056mm for those inserted at 2.5mm/second, a statistically significant difference at p<0.01.

Dr Johansson also examined the impact of pause time – the time the automated injector pauses between loading the lens in the cartridge and injecting it into the eye. At an injection speed of 2.5mm/second, he found no significant difference in wound stretch between a 1.0 second pause and a 3.0 second pause, though mean wound size and stretch were slightly larger in the 3.0 second group.

Dr Johansson noted that the automated injector is controlled by a foot pedal, leaving both hands free to stabilise the globe. The learning curve is short and it simplifies lens insertion. “This is a valuable tool for future cataract surgery through ultra-small incisions.†He echoed Dr Allen in calling for further study on how injection techniques affect wound integrity, appropriate wound architecture and the impact on surgically induced astigmatism.